The parent application, the aforementioned Ser. No. 337,591 is directed to the task of providing an improved wound dressing of simplified construction which maintains a moist environment and prevents scab formation while at the same time obviating the problems which can occur when the wound exudate builds up a pressure bubble beneath the dressing. Such problems include the tendency of the pressure bubble of wound exudate to undermine the adhesive seal to the skin, the resulting increased possibility of contamination of the wound, and the messiness inherent in the escape of wound exudate from the dressing.
In accordance with the invention described and claimed therein, the task is solved in an elegant manner by providing a dressing comprising a base sheet having an opening for placement over the wound; means for securing the base sheet to the skin; and vent means for providing controlled leakage of wound fluid along a path from the wound through the opening of the base sheet, the vent means permitting passage of wound fluid therethrough while reducing evaporation through the opening and thereby helping to insure a moist environment when excess wound fluid is removed from the wound. In a preferred embodiment, the vent means comprises a vent sheet secured to the base sheet over the opening and having a raised portion defining at least one channel extending from the opening to an edge of the vent sheet, the channel communicating with at least one opening permitting the fluid to be vented to the outer surface of the dressing. The opening(s) for venting the fluid may be provided by permitting at least one and preferably two opposed edges of the vent sheet to be free of attachment to the base sheet.
Various embodiments of the vented sheet dressings are described and illustrated in the accompanying drawings.
In the embodiments such as are illustrated in FIGS. 16 and 17 of copending application Ser. No. 337,591 filed Apr. 13, 1989; the wound fluid leaks from the channel through the unsealed edges to the outside of the dressing where it comes in contact with the outside air as well as bacteria or other external contaminants which may be present.
In other embodiments such as are illustrated in FIGS. 1-3, an absorbent layer such as a gauze sponge for receiving and retaining the wound fluid may be located over the back surface of the base sheet and over the vent sheet. As disclosed, a back film of a bacteria impervious material may be secured to the back surface of the absorbent layer.
In still another embodiment, as shown in FIGS. 6 and 7 of copending application Ser. No. 337,591 filed Apr. 13, 1989; a fabric layer impregnated with an antimicrobial agent is secured around its periphery to the back surface of the base sheet. A fluid-impervious cover sheet is secured to the front surface of the fabric layer, i.e. between the fabric layer and the base sheet. The cover sheet is free of attachment to the base sheet and serves as a vent through which fluid can leak and be wicked to the fabric layer.
In summary, the parent case discloses embodiments wherein the wound fluid is present on the outer surface of the dressing. While fully satisfying the objectives of the application in obviating the problems which can occur when wound fluid builds up in and on the wound, it nevertheless is not fully satisfactory in all aspects desired for a wound dressing. Specifically, wound exudate is exposed to the environment as well as to contact with any objects which may be present. Moreover, the outer surface is exposed to bacteria as well as other external contaminants including food or liquid which may be spilled by the patent on the wound, which contaminants can adversely affect the healing process.
In other embodiments, e.g. that shown in FIGS. 1-3, a bacteria-impervious material is disposed over the reservoir for retaining the wound fluid.
While such embodiments will serve to prevent ingress into the dressing of external contaminants, they do present one significant problem, namely the ability for the fabric reservoir to reach its optimum potential for receiving wound fluids.
In order to approximate optimum efficiency of receiving and retaining wound fluids, it is necessary to provide means for removal or displacement of air entrained in the interstices or voids of the fabric reservoir. In other words, it is axiomatic that for one fluid (e.g. wound exudate) to be able to diffuse or wick to a given volume of space, any fluid (e.g. air) initially present in this volume of space must first be permitted to be displaced.
The primary task of this invention is to provide an improved vented dressing of the type described in the parent application, Ser. No. 337,591 having a fabric reservoir for wound fluid disposed over the vent sheet, the fabric reservoir having means protecting it from external contaminants, including bacteria, while at the same time permitting entrained air to be removed so as to optimize the efficiency of the reservoir and, in turn, to minimize the number of dressing changes which may be required.